Electrode Potential PYQ

Electrode Potential PYQQ: 5 Potassium manganate (VII) can be used to estimate the percentage of hydrogen peroxide in household bleach. The following unbalanced equation represents the reaction betweenthem.

Balance this equation by putting the appropriate numbers in the spaces above. [1](b) Use data from the Data Booklet to calculate the E cell for the reaction. [1](c) When 0.020mol dm-3 KMnO4 (aq) was added from a burette into an acidified 25.0cm3 sample of H2O2, 15.00cm3 of KMnO4 was required to reach the end-point.

(i) Describe what you would see during this titration, and also at the end-point. [1][A2 Nov 2007 Paper IV Q5]

Q: 1Chlorine gas and iron (II) ions react together in aqueous solution as follows.Cl2 + 2Fe2+ 2Cl - + 2Fe3+(a) The following diagram shows the apparatus needed to measure the Ecell for the above reaction.

(i) In the spaces below, identify what the five letters A - E in the above diagram represent.ABCD E (ii) Use the Data Booklet to calculate the Ecell for this reaction, and hence decide which direction (left to right, or right to left) electrons would flow through the voltmeter V when switch S is closed. [7](b) (ii) A solution of iron (III) chloride is used to dissolve unwanted copper from printed circuit boards. When a copper-coated printed circuit board is immersed in FeCl3 (aq), the solution turns pale blue. Suggest an equation for the reaction between copper and iron (III) chloride and use the Data Booklet to calculate the E for the reaction. [2][A2 June 2008 Paper IV Q1]Q: 1(b) Both KMnO4 and K2Cr2O7 are used as oxidising agents, usually in acidic solution. (i) Use information from the Data Booklet to explain why their oxidising power increases as the [H+ (aq)] in the solution increases. 2(c) Manganese (IV) oxide, MnO2, is a dark brown solid, insoluble in water and dilute acids. Passing a stream of SO2 (g) through a suspension of MnO2 in water does, however, cause it to dissolve, to give a colourless solution. (i) Use the Data Booklet to suggest an equation for this reaction, and explain what happens to the oxidation states of manganese and of sulfur during the reaction. (ii) The pH of the suspension of MnO2 is reduced. Explain what effect, if any, this would have on the extent of this reaction. [4][A2 Nov 2011 Paper 43 Q1]

Q: 1 Zinc chloride is one of the most important compounds of zinc. It is used in dry cell batteries, as a flux for soldering and tinning, as a corrosion inhibitor in cooling towers and in the manufacture of rayon.Draw a fully labeled diagram to show how you could use a standard hydrogen electrode to measure the standard electrode potential, E, of zinc. 6

(b) The electrolysis of zinc chloride can give different electrode products, depending on the conditions used. Suggest the products formed at each electrode in the following cases. One space has been filled in for you. 3[A2 June 2007 Paper IV Q1]

Q: 5Chlorine is manufactured by the electrolysis of brine, NaCl (aq). At the cathode, H2 (g) and OH- (aq) are produced, but the product at the anode depends on the [NaCl (aq)] in the solution. Either O2 (g) or Cl2 (g) is produced.(a) The equation for the cathode reaction is 2H2O (l) + 2e H2 (g) + 2OH- (aq)Starting from neutral NaCl (aq), write equations for the production at the anode of (i) O2 (g) (ii) Cl2 (g) 2

(b) For electrolysis to occur, the voltage applied to the cell must be at least as large as the Ecell, as calculated from standard electrode potentials. Use the Data Booklet to calculate Ecell for the production at the anode of (i) O2 (g) (ii) Cl2 (g) 2(c) (i) By using one of the phrases more positive, less positive or no change, use the equations you wrote in (a) to deduce the effect of increasing [Cl- (aq)] on the Eanode for the production of O2 (g) the Eanode for the production of Cl2 (g) (ii) Hence explain why the Cl2 (g) : O2 (g) ratio increases as [NaCl (aq)] increases. 3

(d) Sodium chlorate (V) is prepared commercially by electrolysing NaCl (aq) in a cell which allows the cathode and anode electrolytes to mix.The cathode reaction is the same as that described in (a).The equation for the anode reaction is

(i) Construct an ionic equation for the overall reaction. (ii) Calculate the mass of NaClO3 that is produced when a current of 250A is passed through the cell for 60minutes. 4[A2 Nov 2010 Paper 43 Q5]